A DEEP-WATER PATELLOGASTROPOD FROM OLIGOCENE WATER-LOGGED WOOD OF WASHINGTON-STATE, USA (ACMAEOIDEA, PECTINODONTA)

Late Oligocene concretions from the shores of the Strait of Juan de Fu ca, Washington State, USA contain limpets that represent the earliest record of the taxon Pectinodonta. Assignment of these specimens to thi s taxon is based on scanning electron microscopy of shell microstructu re and their intimate association with fossil wood. Shell microstructu res in the Pectinodonta consist of an outer calcitic homogeneous/simpl e prismatic layer followed by a calcitic foliated layer, an aragonitic comarginal crossed lamellar layer, myostracum, and an aragonitic cone complex crossed lamellar layer. A size class analysis of pectinodonti ds from different pieces of fossil and Recent wood suggests that few c ohorts are found on any single piece of wood, and we speculate about p ossible factors that may produce this pattern. Lastly, we describe Pec tinodonta palaeoxylodia Lindberg & Hedegaard new species and associate d taxa from this water-logged wood community.